There is known a magnetic random access memory (MRAM) as one of resistance change type memories. Writing methods of MRAMs include a magnetic field writing method and a spin transfer writing method. Of these methods, the spin transfer method is advantageous in increasing an integration density, reducing power consumption and enhancing capabilities, since this method has such a characteristic that a spin transfer current that is necessary for magnetization reversal decreases as the size of a magnetic body becomes smaller.
An MTJ (Magnetic Tunnel Junction) element of the spin transfer writing method has a multilayer structure which is composed of two ferromagnetic layers and a nonmagnetic barrier layer (insulation thin film) interposed therebetween, and digital data is stored by a change in magnetic resistance due to a spin polarization tunnel effect. The MTJ element may take a low resistance state and a high resistance state by a magnetization orientation of the two ferromagnetic layers. When the magnetization orientation (spin direction) of the two ferromagnetic layers is in a parallel state (P (Parallel) state), the MTJ element is in the low resistance state. When the magnetization orientation of the two ferromagnetic layers is in an antiparallel state (AP (AntiParallel) state), the MTJ element is in the high resistance state.